The present invention relates to a substrate polishing apparatus for polishing a substrate to be polished, including a semiconductor wafer and so on. More particularly, the present invention relates to a substrate polishing apparatus having a film thickness monitor device for continuously monitoring a state of a film thickness of a thin film on a surface to be polished of the substrate (including but not being limited to the state of the film thickness and a state of the film thickness remaining on the surface) in real time during polishing with the substrate polishing apparatus.
Conventional techniques for monitoring a film thickness of a thin film on a substrate for use with a substrate polishing apparatus include, for example, a film thickness monitor device for monitoring a film thickness of the thin film on a substrate, as disclosed in JP-A-2001-235311 (Japanese Patent Public Disclosure). This apparatus is configured to monitor a film thickness of a thin film on the surface of a substrate on the basis of an intensity of reflected light. Water flows in a columnar form along the surface of the substrate to be polished, and the surface thereof is irradiated with an irradiation light, and the irradiated light is reflected from the surface through the flow of water to be received by an optical fiber.
One aspect of a conventional substrate polishing apparatus is constructed as described above. However, a problem exists with such an apparatus in that water flowing in columnar form over a surface to be polished is not stable at a contact point with the surface and tends to vary, thus making it difficult to reliably and accurately monitor a film thickness of a thin film on the surface of the substrate film using reflected irradiated light.
As a similar technique, there is proposed a polishing-end-point detection mechanism as disclosed in JP-A-2001-88021. This mechanism is composed of an optical fiber mounted in a depression in the surface of the table so as to face a light-irradiating and light-receiving surface at one end thereof, and a flow path for feeding a washing liquid, the path having one end opening in the depression. By this configuration, while the washing liquid is being fed into the depression through the flow path, the surface to be polished of a wafer is irradiated with light through the washing liquid in the depression from the optical fiber, and the light reflected on the surface is received through the washing liquid and the optical fiber in the depression. The polishing-end-point is then detected on the basis of surface information about the surface of the substrate obtained from the reflected light.
However, a problem also exists in this art in that a washing liquid may flow in the depression in an irregular way when fed through the flow path. This is a particular problem when the washing liquid is fed through a porous member. In such a case, polishing grains contained in a polishing liquid, polished chips of the wafer, polished chips of a polishing pad, and so on enter the depression, and obstruct transmission and reception of irradiated light. Thus, information about the surface of the substrate cannot be obtained with high accuracy.